Stephanie Keith/REUTERS
Police use a water cannon on protesters near the Standing Rock Indian Reservation in North Dakota, on November 20, 2016.
After months of protest against the proposed North Dakota Access Pipeline, the clash between police and activists heated up Sunday night as temperatures cooled to dangerous levels.
Protesters, many of whom are from the Standing Rock Indian Reservation, have been demonstrating against the oil pipeline that would pass through North Dakota's Lake Oahe, a sacred burial site and major source of drinking water for the Standing Rock Sioux.
Here's what happened on Sunday: